skewness

  1. P

    calculating and interpreting SD from mean and SEM

    I have some summary stats on people's drink intake and I'd like to work out the variance. Frustratingly I have no access to the full data set so I'm having to infer the shape as much as possible from a handful of descriptive stats. I have access to the mean amount, the standard error of the...
  2. B

    How to perform reverse score transformations? (non-normal data)

    Hello, Sadly, my data are significantly non-normal, negatively and not positively skewed, so that leaves me, according to some statisticians, with only 1 available option (reverse scoring transformations; log, square root and reciprocal transformations I've heard that work wonders on positively...
  3. M

    How to WEIGHT the adjusted Fisher–Pearson standardized moment coefficient (skewness).

    Hello, I'm using the adjusted Fisher–Pearson standardized moment coefficient formula to calculate the skew of some sample data (it's the same formula that uses Excel - skew()). The problem it's that I need to weight the points in the sample data; because the data should be time-weighted...
  4. M

    Skewness in SPSS - SPSS answers differently in multiple PC

    'm wanna calculate the Skewness of 10 data(number); But SPSS calculate it differently in multiple computer!!! The Numbers: 239.00, 176.00, 235.00, 217.00, 234.00, 216.00, 318.00, 190.00, 181.00, 225.00. I followed this steps: Analysis--->Descriptive...
  5. W

    mean+standard deviation+skewness+kurtosis

    hi I want to order some variables according to (mean+standard deviation+skewness+kurtosis) or some new rule considering mean value, standard deviation, skewness and kurtosis simultaneously. Is there any similar sorting rule like this? Is this equation used in other research ares? thank you.
  6. I

    testing normality

    Can someone help to find the error in my code? I wanted to make a program in R which will tell me if a distribution is normal or not. It should also print a histogram with a density curve. After reading the .csv file and required packages (moments and ggplot2) i test my data for normality with...
  7. T

    Stochastic Model Validation

    Hi, I am working on a model that takes in a stochastic time series (turbulent velocity) as input and produces n time series outputs. Since the inputs have a stochastic component, every ensemble (or every run of the model) produces slightly varying outputs. Now I want to validate my model by...
  8. K

    Skewed Continuous Predictor - dichotomize or treat as continuous?

    Hello All, I have two scales with 7 binary items. The simple raw scores from these scales (summing the item responses of 0 or 1) are very skewed with about 56% of the sample having a scale score of 0. This is not unexpected as the scale measures behavioral problems with higher scale scores...
  9. D

    Comparing skewness and kurtosis of two distributions

    Hi, Until now, I knew that if skewness=0 and kurtosis=3 it means the distribution is as symmetric/as tall as the normal distribution. But in SPSS you have to compare it with 2xStandard error and if it is smaller it means that there is no asymmetry and kurtosis. Now, my question is, how can I...
  10. P

    Error on the standard deviation, skewness & Kurtosis

    Dear all, Given a sample of N points extracted from a distribution, I would like to know how to estimate the error on the higher moments of the distribution, such as the standard deviation, the skewness and kurtosis. In other words, I know the error on the mean is simply sigma/sqrt(n), but...
  11. M

    Equality of variance and skewness test

    Hi all, I have a data set with 8 repeated measures (i.e., 8 time periods) for each subject and subjects are allocated to two independent groups. I would like to test: 1) whether equality of variance of a dependent variable is different between two groups? 2) whether the skewness...
  12. J

    Should you transform skewed data when the distribution is expected?

    Hi all, I have been discussing this topic all week with people in my department and I can't seem to get a straight answer. I also tried posting this thread in a non-psychology forum and received only a few straight of the textbook responses about positive skew. I was taught long ago that you...
  13. J

    Estimating values from kurtosis and skewness

    If I know the size of a population, the number of categories/labels, and the skewness and kurtosis of the distribution, is it possible to estimate the number of items which fall into each category? For example, given the data set: category A: 11 category B: 13 category C: 15 category D...
  14. M

    Skewness/kurtosis in a spatial regression analysis

    Hi, I'm currently conducting a spatial regression analysis. I'm trying to decide whether my response variable needs to be log transformed. I understand that regression analyses assume normality of the residuals. I also understand that the best way to calculate how close to normality the data...
  15. S

    Finding z score of skewness and Kurtosis

    Dear all, I'm studying stat from Andy Field's "DISCOVERING STATISTICS USING SPSS" 3rd ed. In chapter 5 (Exploring assumptions) page 138 the writer said "To transform any score to a z-score you simply subtract the mean of the distribution (in this case zero) and then divide by the standard...
  16. H

    How do you calculate Skewness? Not the simple case...

    Hello, To begin with I would like you to take into account that I'm not a maths genius, but I understand maths to a good degree. My question is how do you find skewness in univariate probability distributions that are both asymmetric and multimodal? I have two columns of raw data: x - Plotted...